The present invention relates to the technical field of a method and an apparatus for photoelectrically reading original images, particularly images recorded on films.
Heretofore, the images recorded on photographic films such as negatives and reversals (which are hereunder referred to simply as xe2x80x9cfilmsxe2x80x9d) have been commonly printed on light-sensitive materials (photographic paper) by means of direct (analog) exposure in which the film image is projected onto the light-sensitive material.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing operations to produce image data for recording purposes; recording light that has been modulated in accordance with the image data is used to scan and expose a light-sensitive material to record a latent image, which is subsequently developed to produce a (finished) print. The printer operating on this principle has been commercialized as a digital photoprinter.
In the digital photoprinter, images can be processed as digital image data to determine the exposing conditions for printing; therefore, the digital photoprinter is capable of performing effective image processing operations such as the correction of washed-out highlights, or flat or dull shadows due to the taking of pictures with backlight or an electronic flash, and sharpening, and this enables the production of high-quality prints that reproduce images of the quality that has been impossible to achieve by the conventional direct exposure technique.
In addition, not only the assembling of images and the splitting of a single image into plural images but also the composing of characters can be performed by processing the image data and, as a result, prints can be outputted after various editing and/or processing operations have been performed in accordance with specific uses. Outputting images as prints (photographs) is not the sole capability of the digital photoprinter; the image data can be supplied into a computer or the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
The digital photoprinter is basically composed of: a scanner (one of an image reading apparatus) that irradiates reading light to a film and photoelectrically reads an image recorded on the film by an image sensor such as a CCD sensor by sensing the light projected from the film; an image processing apparatus that performs predetermined image processing on image data captured by the scanner or supplied from a digital camera or the like to produce image data for image recording, that is, exposure conditions; a printer (image recording apparatus) that forms a latent image on a light-sensitive material by scan exposing it in accordance with the image data output from the image processing apparatus; and a processor (developing apparatus) that performs development processing on the light-sensitive material exposed by the printer to produce a (finished) print on which the image is reproduced.
In order that such a digital photoprinter outputs prints on which high-quality images are reproduced, it is necessary to obtain as much image information as possible from a film as an original and it is therefore necessary to read images at high resolution. To do so, it is desirable to read the range of all densities of an image recorded on a film by making the maximum use of the dynamic range of a scanner (image sensor).
On the other hand, to reproduce an appropriate image, it is necessary to read the range of all densities of an image recorded on a film by a scanner. However, images in a considerably wide range of densities may be recorded on films; some images may be appropriately exposed but others may be overexposed or underexposed, whereas the dynamic range of a image sensor is limited.
In short, presently, it is very difficult to read all images at high tone resolution in one reading condition.
For this reason, the scanner performs prescan to roughly read images before image reading (fine scan) for obtaining output image data, and sets reading conditions of fine scan in accordance with image data (prescanned data) obtained in the prescan.
To be more specific, in prescan, images are read, even in low tone resolution, under reading conditions that ensure the reading of all images. The obtained prescanned data is used to set reading conditions of the fine scan such that the output of the image sensor is saturated at a slightly lower density than the minimum density of the image of interest, and in fine scan images are read under the thus set reading conditions of the fine scan. By this method, the dynamic range of the image sensor is used to the maximum extent to provide for images having a variety of densities including underexposure and overexposure, thereby achieving image reading at high tone resolution.
Normal photoprinters use prescanned data to set image processing conditions including fine scanned data in an image processing apparatus and the like.
To improve the efficiency of creating prints, it goes without saying that a scanner must efficiently and quickly read images. To achieve this, the quantity (or intensity) of reading light must be increased to provide sufficient reading sensitivity for an image sensor no matter how short photometry time is. As is apparent from the foregoing description, the amount of reading light (light intensity) incident on films is different between prescan and fine scan; it is higher in fine scan.
Although output signal intensity (and image density) from an image sensor is different between prescanned data and fine scanned data because of different reading conditions, it must be basically identical as image data.
However, reading images at the high quantity (or intensity) of reading light would change image density characteristics of films due to heat or other factors and cause a difference in image data between prescanned data and fine scanned data that are different in the amount of reading light, causing deterioration in the quality of output images.
An object of the present invention is to solve the problems of the above described prior art and provide a method and an apparatus for reading images that photoelectrically read original images such as images recorded oh films by two image readings of prescan and fine scan, wherein the differences between image data (density information) obtained by prescan and fine scan can be cancelled out even during image reading at the high quantity of reading light in line with fast reading, and prints on which high quality images are reproduced can be output stably with high productivity by applying the method and apparatus for reading images according to the present invention to a digital photoprinter.
In order to attain the above-described object, according to the present invention, there is provided an image reading method that photoelectrically reads an original image by prescan, sets reading conditions in accordance with prescanned data obtained by the prescan, and performs fine scan that photoelectrically reads the original image to obtain fine scanned data for producing output image data, including:
analyzing both data of a preset area of the original image for both the prescanned data and the fine scanned data to calculate image characteristic values of the prescanned data and the fine scanned data of the preset area;
calculating a correction condition for the fine scanned data such that the image characteristic values of the prescanned data and fine scanned data match; and
processing the fine scanned data on said correction condition.
Preferably, the preset area is a central portion of the original image.
Preferably, the preset area includes a central portion of the original image.
Preferably, the preset area is an area containing a plurality of portions including the central portion selected among a plurality of divided portions to which the original image is divided.
Preferably, the image characteristic value of the preset area is at least one selected from the group consisting of an average density of the preset area, one or more preset density point of a density histogram of the preset area, a highlight point of the preset area and a shadow point of the preset area.
Preferably, the image characteristic value of the preset area is calculated by using both the prescanned data and the fine scanned data which are corrected in device characteristics of means for reading the original image.
Preferably, both the prescanned data and the fine scanned data used for calculating the image characteristic value of the preset area are data subjected to data processing including dark correction, defective image correction and shading correction, data subjected to log conversion or both.
In order to attain the above-described object, the preset invention provides an image reading apparatus for reading photoelectrically an original image that, when reading the image, performs prescan before performing fine scan intended to obtain output image data, and sets reading conditions for the fine scan in accordance with prescanned data obtained by the prescan, including:
prescan analysis device for analyzing prescanned data of a preset area of the original image to calculate an image characteristic value thereof;
memory device for storing fine scanned data obtained by fine scan;
fine scan analysis device for analyzing fine scanned data of the preset area of the original image to calculate an image characteristic value thereof;
correction condition setting device for setting a correction condition for the fine scanned data such that both the image characteristic values calculated by the prescan analysis means and said fine scan analysis means match; and
corrector means for reading the fine scanned data from said memory means and correcting the read fine scanned data in accordance with the correction condition set by the condition setting means.
Preferably, the prescan analysis device and the fine scan analysis device calculate the image characteristic values by using the prescanned data and the fine scanned data corrected in device characteristics of the image reading apparatus.
Preferably, the preset area of the original image has a plurality of portions including a central portion.
Preferably, the image characteristic value is at least either an average density of the preset area, one or more preset density point of a density histogram of the preset area, or both.